Before Joker - Harleen Quinzel
Harleen had a relatively normal life through her teens and early twenties, graduated med school in her mid twenties, and landed her job at Arkham Asylum soon after. Her superior was a misogynistic asshole, so he put her in charge of attempting to rehabilitate a patient known as Joker. This backfired, tremendously.
Harley Quinn and Mistah J
Through her attempts to understand and help Joker get better, he preyed on her own weaknesses, as well as her own hidden mental health issues. In other words, he made her worse when he broke her. Of course, he had manipulated her into thinking everything, every crime they committed, was just a fun game. For two years, Harley and Joker were the perfect clown couple.... On the outside.
Harley always wanted to be a mother, in part due to her rocky relationship with her own. Unfortunately, every time she'd wind up dragged back to Arkham, she'd be given a termination if she came back pregnant. This was done as Arkham staff believed Harley would have been an unfit mother due to her mental state. Sadly, the damage done has left her unable to conceive again.
A Death in The Family is a Chance for Sanity
It was all a game to her, as he made her think, until the death of Jason Todd. For Harley, knowing that she had a hand in the death of a child was enough to wake her up from this chaotic nightmare. She left Joker behind, turning herself in. Harley was sent to a different psychiatric facility, not Arkham, and after about a year of residential treatment, she was deemed rehabilitated enough to move into a group home, which allowed her to slowly reintegrate into society as a functional adult.
Now? Free as a Bird with Unclipped Wings.
By this point in her story, it's been about twelve years since she met Joker. She reached out to the Bats and made amends for her wrongdoings, now working with them when they need additional hands on deck. She has an apartment now, all her own, with space for Bud and Lou. She works for a nonprofit organization dedicated to helping women escape abusers. She's also going back to school part time, trying to get her license reinstated, with the goal of opening a private practice.
Oh yeah, and she's dating again, finally!